Wikipedia says Sodapoppin first popularized Among Us on Twitch in July 2020.
Sodapoppin is the online name of Chance Morris, a prominent Twitch streamer. Although Among Us had launched in 2018, it initially attracted relatively little attention. Its breakthrough came during the COVID-19 pandemic, when viewers and creators sought easy-to-watch multiplayer games that enabled social interaction while people were physically separated.
According to the account summarized by Wikipedia, Sodapoppin streamed the game to a large Twitch audience in July 2020. Other major creators soon followed, including xQc, Pokimane, Shroud, Ninja, MrBeast, Disguised Toast, and PewDiePie. Their broadcasts helped turn the game’s social deduction mechanics into a highly shareable spectacle.
The wording “first popularized” does not mean Sodapoppin was the only early influence. Wikipedia also notes that creators in South Korea and Brazil helped drive interest before the game’s wider English-language Twitch explosion. The fair canonical answer to this specific Wikipedia-based question is Sodapoppin.